Sunday, 27 May 2012

Palaeochat: 1

Over at Archosaur Musings, Dave Hone has been publishing Academics on Archosaurs in which various palaeontologists are asked the same five questions about palaeontological research – past, present and future. One of these featured Jerry Harris and Jerry made a wonderful observation regarding something that has been a continual bane of contention in palaeontology – the use of extant analogies.

When a dinosaur has been discovered, and has gone through the long process of excavation, preparation and description, then the palaeontologist quite often reaches an impasse when it comes to suggesting physiological and anatomical adaptions and especially behavioural patterns. Faced with this degree of uncertainty palaeontologists’ often make inferences based on similarities in animals that they are familiar with today – the extant analogy (EA).

When the EA demonstrates adaptions that the fossil taxon does not then these missing properties in the fossil taxon can then be the object of an inferred analogy. The problem with this, however, is that analogical inferences are often guided by established constraints that allow the palaeontologist to make selected inferences – and herein lays the problem. Just what these constraints are is a matter of conjecture.

This suggests that more palaeontologists are likely to make confident assumptions when they recognise the EA and fossil taxon as similar as they are to disregard them. Of course this is a natural thing to do and we have all done it – we want to see the similarities so that we can envisage our fossil specimens as living breathing animals. This is because common characteristics increase the recognised similarity of two species whereas different traits reduce the recognised similarity. And the more characters shared between the two species, the stronger both our inferences become and similarity appears to be.

Of course, this is not a criticism of, for example, the extant phylogenetic bracket – not by a long way but it does not hurt to be always questioning ourselves when we make perceived assumptions because of similarity. We can hypothesise about various inferences based upon characters found in the EA which are not preserved in the extinct taxon but this must always be quantified by additional phylogenetic, morphological and osteological analysis and, even then, there must be a further rigorous reappraisal of data before drawing any reasonable conclusion. And, even after all this, there will still be a degree of speculation.

Behavioural inferences are speculative in the extreme. Similar physical adaptions and characteristics may appear to suggest a similar lifestyle for an extinct taxon – take the heron-like analogy for Spinosaurus in Planet Dinosaur. But this is completely untestable speculation and, as Jerry Harris stated, non-avian dinosaurs are a totally unique group of animals with no real extant analogues and so the challenge is to concentrate on what made the dinosaurs unique within a much bigger framework that includes everything from the animals themselves to the environment they lived in.

Moving on and Jon Tennant over at Green Tea and Velociraptors recently made a critical appraisal of the very well publicised paper that suggested that methane produced by sauropods could have contributed to a global temperature increase in the Mesozoic. Plenty of other people have made their feelings clear regarding this paper and I’m not about to review it further but Jon made the following observation:

“The amount of times statements are preceded by ‘could have’ ‘suggests’, ‘estimates’, ‘likely’, etc. is an immediate trigger for concern. There’s nothing actually concrete in the paper.”

And yet these words and phrases are universally used in the world of paleontology and with good reason. I suspect that no matter how solid your research may be, how thorough the data analysis is, even how testable a hypothesis may be , it is natural for authors to quantify any statement they make – especially when it is presented to an ever growing audience that has an insatiable need for more and more knowledge. An ever more critical audience too it has to be said.

As a blogger I have become very aware of this phenomenon. So when I review a paper or discuss a conference I do indeed tend to use the words “suggest”, “hypothesise” or “likely” purely because to state anything as fact is guaranteed to set you up for a grilling from a very discerning audience. I still have the odd lapse but I can rely on my readership to point it out - that’s for sure.

Even when I feel certain that a theory is probably correct, and ascribe to it with confidence, I will still describe it as likely or possible. For me, if some research appears correct in my eyes and I can see how the theory was arrived at, I am very likely to subscribe to the premise of the paper and be confident in its testability. However, if a subsequent theory by another palaeontologist is able to disprove the first paper and I am satisfied with the data analysis presented, then I am happy to ascribe to it from that moment on. This does not mean that the previous paper suddenly becomes insignificant or useless but further research has built on the original findings presented and the new paper often uses this data to formulate a new premise. This is the very crux of good science and long may it continue.

It is also another reason not to use those words which state theory and hypotheses as fact and it makes sense to be neutral and impartial. I am, on occasion, shocked by the aggression shown by some paleontologists’ to another’s research when it is published. I’m not talking about these odd papers that crop up from time to time that we all know are full of, how shall we say, dubious information but those papers that are from reputable researchers, which have gone through the peer review process and published in entirely legitimate journals. This is unfortunate and, in my eyes, entirely unnecessary. Constructive criticism yes but when it degenerates into a slanging match in the palaeontological public eye then I’m not interested - what’s the point in that?

Which brings me to my final thought for now and it directly relates to the previous point. I have been asked a couple of times why I do tend to sit on the fence and that I never actually criticise anyone. Well that’s not strictly true and I learnt my lesson a few years back when I opened my mouth a bit too freely on a couple of occasions and was promptly reprimanded by a couple of seasoned palaeontologists – and rightly so (thanks for that guys – you know who you are).

When I took a step back and thought about it I soon realised the truth. Who am I to openly criticise someone’s research that, in all probability, took years to produce? These researchers had endured years of sacrifice, toil and expense to get where they are today and produce the literature that I love to read. Not for me to criticise anything these palaeontologists’ do and more power to them I say, even if I do not necessarily agree with the data presented – they have my utmost respect. I am reminded of the old saying “I do not agree with what you say but I will defend your right to say it”.

However, that does not mean there are those papers which, in my humble opinion, are pretty average and where, again in my opinion, the data provided does not necessarily add up. But this paper is still a valid and peer reviewed contribution to the literature and must be respected as such. There are exceptions and I have no qualms about savaging those so called publications such as the notorious kraken and aquatic dinosaur debacles. But then, in these extreme circumstances, we all do don’t we?

8
comments:

1stly, it reminds me of a similar blog post by Hone ( http://archosaurmusings.wordpress.com/2009/12/07/extrapolating-behaviours-–-picking-the-right-analogue/ ) which in turn reminds me of an article by Holtz ( http://web.me.com/dinoruss/jdp/trex/hunting.htm ). More specifically, Holtz had already found good extant analogues for (Quoting Hone) "the predatory behaviour of theropods".

2ndly, it reminds me of GABRA ( http://penchant4paleo.blogspot.com/2010/09/brain-is-wider-than-sky.html ) which may be extant analogue-making at its best.

3rdly, while I get what Harris is saying, I think he's being too conservative, especially given my 2nd comment's Gardom & Milner quote. For a good example of what I mean, compare my 2nd comment's Harris quote (Harris is talking about the Dromaeopodus trackway) to my 2nd comment's Bakker quote (That the Dromaeopodus trackway shows a group of 6 adults hanging out but not hunting is all the more reason to interpret it as evidence of pack behavior). I can't say for sure, but I'm educated-guessing that some paleontologists (E.g. Milner & Bakker) have a better understanding of living animals than others (E.g. Harris) & thus are better judges of the usefulness of extant analogues. Don't get me wrong, though, as I appreciate Harris' work.

Quoting Gardom & Milner ( http://www.amazon.com/Natural-History-Museum-Book-Dinosaurs/dp/184442183X/ref=sr_1_1?s=books&ie=UTF8&qid=1325974924&sr=1-1 ): "Why are they so fascinating? Probably because they seem so amazingly different from the animals we know - bus-sized plant-eaters, hunters with 20 centimetre long serrated teeth, strange creatures with outlandish names. Yet if we only think of dinosaurs as monsters we will never get past the 'Did-you- know? Amazing Facts!' level of knowledge about them. The really compelling fascination of dinosaurs is not how different but how similar they are to the animals we know.Despite their monstrous reputation many dinosaurs were, in fact, no larger than animals that can be found living today. All of them had to meet the same basic challenges of survival. In their search for food and space, their methods of moving and eating and their social organization, dinosaurs show striking similarities to modern groups, particularly birds and mammals. Over the last fifteen years spectacular new discoveries made in the field and laboratory have demonstrated even more clearly how much dinosaurs and todays' animals have in common."

Quoting Harris ( http://scienceblogs.com/laelaps/2008/04/24/paleontological-profiles-jerry/ ): "What the track makers might have been doing (other than ambulating, of course…!) while moving as a coherent group is anybody’s guess. There’s a temptation, I think, to conflate “gregariousness” with “hunting” here – thanks in large part to a recent push from “Jurassic Park” – to want to extrapolate “exciting,” “action packed” interpreted behaviors from the tracks. It’s something we specifically took pains to denounce both in the paper and with the media because it is not evidence for hunting in packs…just moving in groups, at least on occasion. There’s no way to tell from the trackways whether or not the track makers were hunting when they made the tracks, or whether they ever hunted in packs; certainly, the track makers don’t seem to have been in any big hurry; nor do they seem to be “stalking” slowly, but who knows? Still, it’s an evocative portrait…just one that involves using that imagination to move a bit beyond the actual data."

Quoting Bakker ( http://www.amazon.com/Raptor-Pack-Step-into-Reading-Step-5/dp/0375823034/ref=la_B000AP7OMC_1_2?ie=UTF8&qid=1338527221&sr=1-2 ): "Predators don't usually hang out in groups if they don't hunt together. Tigers are like this — they mostly hunt alone, and you don't see bunches of tigers lying around together. But lions are social predators. They hunt and raise their young and sleep and snore together."

Hi Herman - and thanks for the comments. There is nothing intrinsically wrong with using extant analogues to help try and describe behavioural patterns for extinct animals. Seriously, there really isn't.

The problem is that it is entirely subjective. In a recent comment over at Archosaur Musings I described EA's to Jerry Harris as one man's analog being another man's antithesis - and this is why they cause issues.

I have been slaughtered in the past for daring to compare modern ecosystems with ancient ecosystems but I still see the similarities. And since birds are extant dinosaurs, there should be nothing to stop us from inferring behavioural patterns, mating and breeding for extinct dinosaurs.

But the fact is that, despite dinosaurs still having the same basic requirements for survival as todays' living animals, they were still a unique clade of extinct animals with no modern equivalent (birds not included) and were so very different from anything else alive. And let's not forget they lived in totally different environments and ecosystems.

Heck, even the air pressure and atmospheric make up were different and the magnetic pole flipped on occasion as well so there are multiple considerations to take into account when using EA's - it isn't simply comparing the extant with the extinct and saying that they were alike - that is not helpful at all.

Sorry if I came across too strongly/harshly. Again, I completely understand where you & Harris are coming from in that there are several factors to account for when making extant analogues. All I meant to say is that I think some paleontologists (E.g. Harris) are too far on the "antithesis" end of the spectrum & that it may have something to do w/their understanding of living animals compared to that of other paleontologists (E.g. Milner & Bakker).

Hey no apologies necessary! And I agree with what you are saying - getting the balance right between the two "camps" is the trick here and then the extant analog can become a useful comparison tool for sure.

Post a Comment

Search This Blog

Saurian is.....

I am an avocational vertebrate palaeontologist with a particular interest in tyrannosaurids. Fossil preparation, conservation and research also feature high on my agenda.
Currently involved in the day to day running of a progressive and exciting research group - we are hopeful of making a positive contribution to our science.